The present invention relates to aircraft wings and more particularly to an improved aircraft tip device with aileron control.
The use of raked wing tips to improve aircraft dynamics is well known in the art. Traditional swept wing aircraft include a trapezoidal-shaped wing with a single leading edge. For commercial aircraft, the wing sweep angle may be between 0 and 40 degrees. This swept back wing provides advantages by reducing drag at higher speeds. Improvements made to the wing tips have further improved wing efficiency by reducing induced drag.
One method of improving the performance of swept wings is the use of raked wing tips. U.S. Pat. No. 5,039,032 to Rudolph, herein incorporated by reference in its entirety, describes the benefits of a highly tapered wing tip extension added to the tip of an existing swept airplane wing that reduces high speed drag. This tapered wing tip may include a wing sweep of 40 degrees or more. The improvement improves aircraft performance by decreasing induced drag while increasing the aspect ratio of the wing.
U.S. Pat. No. 6,089,502 to Herrick et al., herein incorporated in its entirety, improves on the wing tip extension concept developed in Rudolph by utilizing blunt leading edge raked wing tips. The improved wing tip extensions described in Herrick are useful for aircraft designed to operate at high subsonic Mach numbers (at or greater than 0.7). This application overcomes the need for a leading edge high-lift device (such as a slat) that is required for raked wing tips having a leading edge sweep between 40 and 50 degrees. The inventors in Herrick determined that an aircraft with blunt leading edge raked wingtips therefore improved over the raked wing tips described by Rudolph.
One issue not resolved with such wing tip designs is the changing flight dynamics as an aircraft changes speed, altitude, and flight conditions. A specific area where flight dynamics change is the use of ailerons during takeoff and landing.
Ailerons on an aircraft can be used to modify the roll angle of the aircraft, usually used for turning the aircraft during flight. This is accomplished by changing the magnitude of the roll moments on each wing. For example, to roll an aircraft to the right at low speeds, a left aileron may be positioned to extend below the left wing and a right aileron positioned to extend above the right wing. The downwardly positioned aileron increases lift on the left wing while the upwardly positioned aileron decreases the lift on the right wing. This changes the roll moment, causing the aircraft to roll in the direction of the upwardly positioned right aileron.
At higher speeds, the aircraft may experience control reversal due to the characteristics of the wing and aileron. A downwardly positioned aileron creates a higher lift on the trailing edge of a wing, and at high speeds the lift differential between the leading and trailing edges may cause the wing to twist leading edge down. This twisting causes the aircraft to turn in the direction opposite of what was intended. The control reversal speed is the point at which this control reversal occurs. However, control of the aircraft near this control reversal speed may be sluggish or nonresponsive. The chord length of the wing, position of the aileron relative the aircraft fuselage, and thickness of the wing are all factors in determining the control reversal speed.
In commercial aircraft, ailerons positioned near the tips of the aircraft (outboard ailerons) are useful for low-speed maneuvers, but the control reversal speed is sufficiently low that control reversal has occurred by the time the aircraft reaches cruising speed. In order to avoid the issue of control reversal and avoid sluggish or nonresponsive control, secondary (inboard ailerons) may be disposed inboard of the outboard ailerons. Because of their position on the wing, the control reversal speed is increased as the force differential required to twist the wing is increased. However, the amount of energy required to operate these inboard ailerons may be increased as the lift differential is not as great, and the operation of these inboard ailerons may create more drag.
Additionally, for any given aircraft condition, based on weight, geometry, airspeed and atmospheric conditions, there is an ideal lift distribution where induced drag is minimized. The geometry of an aircraft is generally fixed, based on the wing geometry, airfoil shape, chord length and wingspan. Other conditions, including weight and atmospheric conditions, are generally uncontrollable during the flight as well. Therefore, the lift distribution of the aircraft must be determined for a preferred set of circumstances during design of the aircraft.
A final area where improvements may be made is in the use of wingspan. As is well known in the art, the wingspan of an aircraft has a significant impact on the efficiency and lift distribution of an aircraft in flight. However, aircraft wingspans may be limited by space considerations at airports. A wide wingspan may be preferable, but may not always be acceptable due to space considerations between airport gates or in hangars, for example.
Therefore, there is realized in the art a need for an aircraft with increased efficiency while maintaining the wingspan requirements of airports.
There is further realized a need in the art a novel method and apparatus for improving control of aircraft while avoiding sluggish or nonresponsive roll control at or near control reversal speed.
There is further realized a need in the art for control mechanisms that avoid the issue of control reversal which may lead to pilot confusion.
There is further realized a need in the art for an aircraft that is capable of altering the lift distribution on the aircraft so as to approach an ideal condition.